Tension members

Abstract

Prestressed composite tension members comprise an assembly which includes compression and tension portions which are loaded longitudinally along or symmetrical with the center of gravity of the compression portion and prestressed causing both the tension and compression portions to cooperate in resisting lengthening of the assembly rather than the tension portion alone, thus lessening such elongations. In one embodiment, the tension member forms a tension member in a truss, having an upper chord and vertical webs acting in compression, and the tension member comprises a tensioned cable mounted within a series of abutting, slotted and glued wood members under compression. In another embodiment, the tension member comprises a tensioned cable centered in a plurality of tubes in compression, forming the truss lower chord. In another truss, the lower chord consists of the tension member comprised of a tensioned cable centered in a slotted wood member under compression with the end cable grips bearing on a bearing plate at the end of the compression member. In another truss lower chord, the tension member consists of a tensioned cable centered in a slotted wood member under compression with the end cable grips bearing on a plate at the end of the truss heel assembly. In another truss embodiment, the tension member comprises a tensioned, high strength, steel strap encircling the sides and ends of the wood compression member. In another embodiment, the tension member comprises tensioned cables centered in a slotted, glued-laminated compression member, such tension member forming the main structural elements of the roof system. In another, a plurality of tension members having tensioned cable cores and tubes in compression and connecting a central ring to an outer ring create a tension structure. In another embodiment, a tension-compression structure is created and comprises a tensioned cable centered in a slotted, glued-laminated, compression portion. In another embodiment, a mechanism, capable of supporting a substantial load at its end, comprises metal tubes abutting a high friction material abutting spherical balls allowing mobility and the ability to assume many different positions.

What is claimed is: 
     
       1. In an improved composite tension member, a plurality of end-to-end segments having a longitudinal center of gravity, each segment including a pair of wood beams fastened together in face-to-face engagement, said segments comprising an elongated compression portion, said segments meeting at included angles to each other of less than 180°, said segments providing a longitudinal passageway extending therethrough;   elongated tension means disposed in said passageway, said tension means paralleling and being symmetrical relative to said longitudinal center of gravity and engaging the ends of said compression portion,   said tension means being normally under a preloading predetermined tension in sufficient magnitude to press against the ends of said compression portion to place and maintain said compression portion under compressive stress throughout the application of all contemplated external tension loading conditions on said tension member, thereby causing both said tension means and said compression portion to cooperate in resisting lengthening of the assembly rather than said tension means alone, thus lessening such elongation,   said tension means including a pair of abutment members engaging the extreme outer ends of said compression portion, said tension means also including anchoring devices abutting said abutment members;   and at least one connecting means engaging the tension means and the end portions of the compression segments to prevent crushing of the compression portion by the tension means.   
     
     
       2. The composite tension member of claim 1 wherein the connecting means are metal plates fitting in slots in the end portions of the segments. 
     
     
       3. The composite tension member of claim 1 including a plurality of bearing plates abutting the ends of the segments and accommodating passage of the tension means. 
     
     
       4. In a truss, a compression chord,   a pair of end assemblies each having a first abutment engaging one end of the compression chord and also including a second abutment,   a prestressed tension chord including a compression portion in abutment with the second abutments and having at least one passage extending therealong,   the tension chord also including at least one tension means extending along the passage or passages and secured to the second abutments under tension to preload the compression portion to an amount sufficient to maintain it under compression under all contemplated external loading conditions on the truss,   the compression portion including a plurality of segments forming angles with each other of less than 180°,   the tension chord also including connecting means engaging the tension means and the end portions of the compression segments at the joints thereof to prevent crushing of the compression portion by the tension means,   and at least one web connected to the compression chord and the tension chord.   
     
     
       5. The truss of claim 4 wherein the connecting means comprise a plurality of plates, the end portions of the compression segments having the plates embedded therein. 
     
     
       6. The truss of claim 5 wherein each compression segment has slots therein receiving the plates. 
     
     
       7. The truss of claim 4 wherein each of the end assemblies comprises a pair of straps extending along and fastened to the compression chord, a first abutment plate secured to the straps at points spaced substantially from both ends of the straps, and a second abutment plate spaced from the first abutment plate and facing downwardly below the first abutment plate and secured to the straps. 
     
     
       8. In a truss, a compression chord,   a pair of end assemblies each having a first abutment engaging one end of the compression chord and also including a second abutment,   a prestressed tension chord including a plurality of segments angularly abutting each other and having longitudinally extending passages to accommodate the tension means,   said segments having at least one longitudinal passage therethrough,   the tension chord including tension means centered relative to the center of gravity of said segments and extending along the passage or passages and secured to the second abutments under sufficient tension to preload said segments to an amount sufficient to maintain compression under all contemplated external loading conditions on the truss,   a plurality of pads between the end portions of said segments,   and at least one web connected to the compression chord and the tension chord.   
     
     
       9. In a truss, a compression chord,   a pair of end assemblies each having a first abutment engaging one end of the compression chord and also including a second abutment,   a prestressed tension chord including a plurality of segments angularly abutting each other and having longitudinally extending passages to accommodate the tension means,   the tension chord including tension means centered relative to the center of gravity of the segments and extending along the passage and secured to the second abutments under sufficient tension to preload the segments to an amount sufficient to maintain compression under all contemplated external loading conditions on the truss,   at least one metal plate positioned between the end portions of each of the segments and engaged by the ends thereof,   and at least one web connected to the compression chord and the tension chord.